1. Field of the Invention
The present invention relates to machines and method, according to which advancing wire, material of prismatic cross-section, or rod material may be gripped in a suitable manner, so that they are not displaced from the geometrical plane of bending at bending machines, or so that they do not undergo torsion while being advanced.
2. Description of Related Art
In a bending machine, the wire, material of prismatic cross-section, or rod material is advanced towards the bending head, where it is bent to a desired angle. The desired shape is produced by sequential advancements and bendings at the desired sizes to produce a product.
In bending machines producing planar shapes it is required that the under-production product be located within the plane of bending. In bending machines producing three-dimensional products, it is required that the bends be effected within specific planes so that there is no distortion of the under-production product displaced outside of the bending planes.
The advanced material—wire, material of prismatic cross-section, or rod material—present tolerances as to their dimensions and as to their mechanical characteristics. Particularly rods may have the characteristics of irregular external surface, of distributed ribs along the rod axis, of longitudinal ribs, of the twisting of longitudinal ribs along the length of the rod, and of the deviation of the cross-section from a perfect circular shape.
When the wire, the material of prismatic cross-section, or the rod material is advanced by rollers, it may twist in relation to the axial line as a result of the deviations of its external dimensions from the perfect circle. Consequently the under-production part twists and is displaced out of the bending plane. In this manner, a two-dimensional product is deformed out of and displaced out of its plane; and a three-dimensional one is distorted as the bending planes are displaced.
Furthermore, during the production of three-dimensional products, as the product is produced in the production space there is displacement of the center of mass in the production space and this same product mass of the product causes torsion of the wire, the prismatic material, or the rod material, so that finally there is undesirable distortion of the under-production product.
In straightening machines with rotors, rollers, or dies the material being straightened may rotate during straightening. Thus, even though the rotor effects straightening of high quality, it cannot be used as a straightening unit in bending machines because of the rotation of the under-production part, and the product is bent outside the geometric plane of bending.